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          LV06-12-ConfigFS-03-设备树插件驱动分析
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    <div class="post-body" itemprop="articleBody"><p>设备树插件也是用的configfs，来了解一下？若笔记中有错误或者不合适的地方，欢迎批评指正😃。</p>
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<details class="folding-tag" blue><summary> 点击查看使用工具及版本 </summary>
              <div class='content'>
              <table>    <tr>        <td align="center" rowspan="5">PC端开发环境</td>        <td align="center" width=150px>Windows</td>        <td align="left">Windows11</td>    </tr>    <tr>        <td align="center">Ubuntu</td>        <td align="left">Ubuntu20.04.2的64位版本</td>      </tr>    <tr>        <td align="center">VMware® Workstation 17 Pro</td>        <td align="left">17.6.0 build-24238078</td>      </tr>    <tr>        <td align="center">终端软件</td>        <td align="left">MobaXterm(Professional Edition v23.0 Build 5042 (license))</td>    </tr>    <tr>        <td align="center">Win32DiskImager</td>        <td align="left">Win32DiskImager v1.0</td>      </tr>    <tr>        <td align="center" rowspan="3">Linux开发板环境</td>        <td align="center">Linux开发板</td>        <td align="left">正点原子 i.MX6ULL Linux 阿尔法开发板</td>      </tr>    <tr>        <td align="center">uboot</td>        <td align="left">NXP官方提供的uboot，使用的uboot版本为U-Boot 2019.04</td>      </tr>    <tr>        <td align="center">linux内核</td>        <td align="left">linux-4.19.71(NXP官方提供)</td>      </tr></table>
              </div>
            </details>

<details class="folding-tag" blue><summary> 点击查看本文参考资料 </summary>
              <div class='content'>
              <table>    <tr>        <td align="center">分类</td>        <td align="center">网址</td>        <td align="center">说明</td>    </tr>    <tr>        <td align="center" rowspan="5">官方网站</td>        <td align="left"><a href="https://www.arm.com/" target="_blank">https://www.arm.com/</a></td>        <td align="left">ARM官方网站，在这里我们可以找到Cotex-Mx以及ARMVx的一些文档</td>    </tr>    <tr>        <td align="left"><a href="https://www.nxp.com.cn/" target="_blank">https://www.nxp.com.cn/ </a></td>        <td align="left">NXP官方网站</td>    </tr>    <tr>        <td align="left"><a href="https://www.nxpic.org.cn/" target="_blank">https://www.nxpic.org.cn/</a></td><td align="left">NXP 官方社区</td>    </tr>    <tr>        <td align="left"><a href="https://u-boot.readthedocs.io/en/latest/" target="_blank">https://u-boot.readthedocs.io/en/latest/</a></td><td align="left">u-boot官网</td>    </tr>    <tr>        <td align="left"><a href="https://www.kernel.org/" target="_blank">https://www.kernel.org/</a></td><td align="left">linux内核官网</td>    </tr></table>
              </div>
            </details>

<details class="folding-tag" blue><summary> 点击查看相关文件下载 </summary>
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              <table>    <tr>        <td align="center">分类</td>        <td align="center">网址</td>        <td align="center">说明</td>    </tr>    <tr>        <td align="center" rowspan="3">NXP</td>        <td align="left"><a href="https://github.com/nxp-imx" target="_blank">https://github.com/nxp-imx</a></td>        <td align="left">NXP imx开发资源GitHub组织，里边会有u-boot和linux内核的仓库</td>    </tr>    <tr>        <td align="left"><a href="https://github.com/nxp-imx/linux-imx/releases/tag/v4.19.71" target="_blank">nxp-imx/linux-imx/releases/tag/v4.19.71</a></td>        <td align="left">NXP linux内核仓库tags中的v4.19.71</td>    </tr>    <tr>        <td align="left"><a href="https://github.com/nxp-imx/uboot-imx/releases/tag/rel_imx_4.19.35_1.1.0" target="_blank">nxp-imx/uboot-imx/releases/tag/rel_imx_4.19.35_1.1.0</a></td>        <td align="left">NXP u-boot仓库tags中的rel_imx_4.19.35_1.1.0</td>    </tr>    <tr>        <td align="center" rowspan="2">I.MX6ULL</td>        <td align="left"><a href="https://www.nxp.com.cn/docs/en/data-sheet/IMX6ULLIEC.pdf" target="_blank">i.MX 6ULL Applications Processors for Industrial Products</a></td>        <td align="left">I.MX6ULL 芯片手册（datasheet，可以在线查看）</td>    </tr>    <tr>        <td align="left"><a href="https://www.nxp.com.cn/webapp/Download?colCode=IMX6ULLRM&lang_cd=zh" target="_blank">i.MX 6ULL Applications ProcessorReference Manual</a></td>        <td align="left">I.MX6ULL 参考手册（下载后才能查看，需要登录NXP官网）</td>    </tr>    <tr>        <td align="center" rowspan="3">Source Code</td>        <td align="left"><a href="https://elixir.bootlin.com/linux/latest/source" target="_blank">https://elixir.bootlin.com/linux/latest/source</a></td>        <td align="left">linux kernel源码</td>    </tr>    <tr>        <td align="left"><a href="https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/?h=v4.19.71&id=e7d2672c66e4d3675570369bf20856296da312c4" target="_blank">kernel/git/stable/linux.git - Linux kernel stable tree</a></td>        <td align="left">linux kernel源码(官网,tag 4.19.71)</td>    </tr>    <tr>        <td align="left"><a href="https://elixir.bootlin.com/u-boot/latest/source" target="_blank">https://elixir.bootlin.com/u-boot/latest/source</a></td>        <td align="left">uboot源码</td>    </tr></table>
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<h1 id="一、源码分析"><a href="#一、源码分析" class="headerlink" title="一、源码分析"></a><font size=3>一、源码分析</font></h1><h2 id="1-dtbocfg-module-init"><a href="#1-dtbocfg-module-init" class="headerlink" title="1. dtbocfg_module_init()"></a><font size=3>1. dtbocfg_module_init()</font></h2><p>先来看模块的初始化函数dtbocfg_module_init()：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * dtbocfg_module_init()</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="type">static</span> <span class="type">int</span> __init <span class="title function_">dtbocfg_module_init</span><span class="params">(<span class="type">void</span>)</span></span><br><span class="line">&#123;</span><br><span class="line">    <span class="type">int</span> retval = <span class="number">0</span>;</span><br><span class="line"></span><br><span class="line">    pr_info(DRIVER_NAME <span class="string">&quot;: &quot;</span> DRIVER_VERSION <span class="string">&quot;\n&quot;</span>);</span><br><span class="line"></span><br><span class="line">    config_group_init(&amp;dtbocfg_root_subsys.su_group);</span><br><span class="line">    config_group_init_type_name(&amp;dtbocfg_overlay_group, <span class="string">&quot;overlays&quot;</span>, &amp;dtbocfg_overlays_type);</span><br><span class="line"></span><br><span class="line">    retval = configfs_register_subsystem(&amp;dtbocfg_root_subsys);</span><br><span class="line">    <span class="keyword">if</span> (retval != <span class="number">0</span>) &#123;</span><br><span class="line">        pr_err( <span class="string">&quot;%s: couldn&#x27;t register subsys\n&quot;</span>, __func__);</span><br><span class="line">        <span class="keyword">goto</span> register_subsystem_failed;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    retval = configfs_register_group(&amp;dtbocfg_root_subsys.su_group, &amp;dtbocfg_overlay_group);</span><br><span class="line">    <span class="keyword">if</span> (retval != <span class="number">0</span>) &#123;</span><br><span class="line">        pr_err( <span class="string">&quot;%s: couldn&#x27;t register group\n&quot;</span>, __func__);</span><br><span class="line">        <span class="keyword">goto</span> register_group_failed;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    pr_info(DRIVER_NAME <span class="string">&quot;: OK\n&quot;</span>);</span><br><span class="line">    <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line"></span><br><span class="line">  register_group_failed:</span><br><span class="line">    configfs_unregister_subsystem(&amp;dtbocfg_root_subsys);</span><br><span class="line">  register_subsystem_failed:</span><br><span class="line">    <span class="keyword">return</span> retval;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>可以看到，这里和前面我们的demo一样，创建了一个子系统和一个配置项组。</p>
<h3 id="1-1-子系统相关结构"><a href="#1-1-子系统相关结构" class="headerlink" title="1.1 子系统相关结构"></a><font size=3>1.1 子系统相关结构</font></h3><p>子系统 configfs_subsystem 相关的变量如下：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Device Tree Blob Overlay Root Sub System Structures</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="type">static</span> <span class="class"><span class="keyword">struct</span> <span class="title">configfs_group_operations</span> <span class="title">dtbocfg_root_ops</span> =</span> &#123;</span><br><span class="line">    <span class="comment">/* empty - we don&#x27;t allow anything to be created */</span></span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="type">static</span> <span class="class"><span class="keyword">struct</span> <span class="title">config_item_type</span> <span class="title">dtbocfg_root_type</span> =</span> &#123;</span><br><span class="line">    .ct_group_ops   = &amp;dtbocfg_root_ops,</span><br><span class="line">    .ct_owner       = THIS_MODULE,</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="type">static</span> <span class="class"><span class="keyword">struct</span> <span class="title">configfs_subsystem</span> <span class="title">dtbocfg_root_subsys</span> =</span> &#123;</span><br><span class="line">    .su_group = &#123;</span><br><span class="line">        .cg_item = &#123;</span><br><span class="line">            .ci_namebuf = <span class="string">&quot;device-tree&quot;</span>,</span><br><span class="line">            .ci_type    = &amp;dtbocfg_root_type,</span><br><span class="line">        &#125;,</span><br><span class="line">    &#125;,</span><br><span class="line">  .su_mutex = __MUTEX_INITIALIZER(dtbocfg_root_subsys.su_mutex),</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line">configfs_register_subsystem(&amp;dtbocfg_root_subsys);</span><br></pre></td></tr></table></figure>

<h3 id="1-2-配置项组相关结构"><a href="#1-2-配置项组相关结构" class="headerlink" title="1.2 配置项组相关结构"></a><font size=3>1.2 配置项组相关结构</font></h3><p>我们看一下配置项组的相关结构：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Device Tree Blob Overlay Sub Group Structures</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="type">static</span> <span class="class"><span class="keyword">struct</span> <span class="title">configfs_group_operations</span> <span class="title">dtbocfg_overlays_ops</span> =</span> &#123;</span><br><span class="line">    .make_item      = dtbocfg_overlay_group_make_item,</span><br><span class="line">    .drop_item      = dtbocfg_overlay_group_drop_item,</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="type">static</span> <span class="class"><span class="keyword">struct</span> <span class="title">config_item_type</span> <span class="title">dtbocfg_overlays_type</span> =</span> &#123;</span><br><span class="line">    .ct_group_ops   = &amp;dtbocfg_overlays_ops,</span><br><span class="line">    .ct_owner       = THIS_MODULE,</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="type">static</span> <span class="class"><span class="keyword">struct</span> <span class="title">config_group</span> <span class="title">dtbocfg_overlay_group</span>;</span></span><br><span class="line"></span><br><span class="line">config_group_init(&amp;dtbocfg_root_subsys.su_group);</span><br><span class="line">config_group_init_type_name(&amp;dtbocfg_overlay_group, <span class="string">&quot;overlays&quot;</span>, &amp;dtbocfg_overlays_type);</span><br><span class="line"></span><br><span class="line">configfs_register_group(&amp;dtbocfg_root_subsys.su_group, &amp;dtbocfg_overlay_group);</span><br></pre></td></tr></table></figure>

<p>在 dtbocfg_overlays_type 中实现了 ct_group_ops 下的 make_item 和 drop_item。   </p>
<h2 id="2-make-item"><a href="#2-make-item" class="headerlink" title="2. make_item"></a><font size=3>2. make_item</font></h2><p>我们在配置项组中执行mkdir创建一个配置项的时候，会调用dtbocfg_overlay_group_make_item()函数：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * dtbocfg_overlay_group_make_item() - Make Device Tree Overlay Group Item</span></span><br><span class="line"><span class="comment"> * @group: Pointer to Configuration Group</span></span><br><span class="line"><span class="comment"> * @name : Pointer to Group Name</span></span><br><span class="line"><span class="comment"> * Return  Pointer to Device Tree Overlay Group Item</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="type">static</span> <span class="keyword">struct</span> config_item *<span class="title function_">dtbocfg_overlay_group_make_item</span><span class="params">(<span class="keyword">struct</span> config_group *group, <span class="type">const</span> <span class="type">char</span> *name)</span></span><br><span class="line">&#123;</span><br><span class="line">    <span class="class"><span class="keyword">struct</span> <span class="title">dtbocfg_overlay_item</span> *<span class="title">overlay</span>;</span></span><br><span class="line"></span><br><span class="line">    pr_debug(<span class="string">&quot;%s\n&quot;</span>, __func__);</span><br><span class="line"></span><br><span class="line">    overlay = kzalloc(<span class="keyword">sizeof</span>(*overlay), GFP_KERNEL);</span><br><span class="line"></span><br><span class="line">    <span class="keyword">if</span> (!overlay)</span><br><span class="line">        <span class="keyword">return</span> ERR_PTR(-ENOMEM);</span><br><span class="line">    overlay-&gt;id        = <span class="number">-1</span>;</span><br><span class="line">    overlay-&gt;dtbo      = <span class="literal">NULL</span>;</span><br><span class="line">    overlay-&gt;dtbo_size = <span class="number">0</span>;</span><br><span class="line"></span><br><span class="line">    config_item_init_type_name(&amp;overlay-&gt;item, name, &amp;dtbocfg_overlay_item_type);</span><br><span class="line">    <span class="keyword">return</span> &amp;overlay-&gt;item;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>在这个里面我们会创建dtbocfg_overlay_item，然后用 dtbocfg_overlay_item_type 去初始化这个item。</p>
<h3 id="2-1-dtbocfg-overlay-item-type"><a href="#2-1-dtbocfg-overlay-item-type" class="headerlink" title="2.1 dtbocfg_overlay_item_type "></a><font size=3>2.1 dtbocfg_overlay_item_type </font></h3><p>dtbocfg_overlay_item_type定义如下：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Device Tree Blob Overlay Item Structure</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="type">static</span> <span class="class"><span class="keyword">struct</span> <span class="title">configfs_item_operations</span> <span class="title">dtbocfg_overlay_item_ops</span> =</span> &#123;</span><br><span class="line">    .release        = dtbocfg_overlay_release,</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="type">static</span> <span class="class"><span class="keyword">struct</span> <span class="title">config_item_type</span> <span class="title">dtbocfg_overlay_item_type</span> =</span> &#123;</span><br><span class="line">    .ct_item_ops    = &amp;dtbocfg_overlay_item_ops,</span><br><span class="line">    .ct_attrs       = dtbocfg_overlay_attrs,</span><br><span class="line">    .ct_bin_attrs   = dtbocfg_overlay_bin_attrs,</span><br><span class="line">    .ct_owner       = THIS_MODULE,</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>

<p>可以看到，在在 dtbocfg_overlay_item_type 中实现了 attrs 和 bin_attrs 和 ct_item_ops  </p>
<h3 id="2-2-attrs"><a href="#2-2-attrs" class="headerlink" title="2.2 attrs"></a><font size=3>2.2 attrs</font></h3><p>这里定义了两个属性：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * Device Tree Blob Overlay Attribute Structure</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line">CONFIGFS_BIN_ATTR(dtbocfg_overlay_item_, dtbo, <span class="literal">NULL</span>, <span class="number">1024</span> * <span class="number">1024</span>); <span class="comment">// 1MiB should be way more than enough</span></span><br><span class="line">CONFIGFS_ATTR(dtbocfg_overlay_item_, status);</span><br><span class="line"></span><br><span class="line"><span class="type">static</span> <span class="class"><span class="keyword">struct</span> <span class="title">configfs_attribute</span> *<span class="title">dtbocfg_overlay_attrs</span>[] =</span> &#123;</span><br><span class="line">    &amp;dtbocfg_overlay_item_attr_status,</span><br><span class="line">    <span class="literal">NULL</span>,</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="type">static</span> <span class="class"><span class="keyword">struct</span> <span class="title">configfs_bin_attribute</span> *<span class="title">dtbocfg_overlay_bin_attrs</span>[] =</span> &#123;</span><br><span class="line">    &amp;dtbocfg_overlay_item_attr_dtbo,</span><br><span class="line">    <span class="literal">NULL</span>,</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>

<p>每个属性都会有自己的操作函数。</p>
<h4 id="2-2-1-dtbocfg-overlay-item-attr-dtbo"><a href="#2-2-1-dtbocfg-overlay-item-attr-dtbo" class="headerlink" title="2.2.1 dtbocfg_overlay_item_attr_dtbo"></a><font size=3>2.2.1 dtbocfg_overlay_item_attr_dtbo</font></h4><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * dtbocfg_overlay_item_dtbo_write() - Write Device Tree Blob to Configuration Item</span></span><br><span class="line"><span class="comment"> * @item : Pointer to Configuration Item</span></span><br><span class="line"><span class="comment"> * @page : Pointer to Value Buffer </span></span><br><span class="line"><span class="comment"> * @count: Size of Value Buffer</span></span><br><span class="line"><span class="comment"> * return  Stored Size or Error Status.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="type">static</span> <span class="type">ssize_t</span> <span class="title function_">dtbocfg_overlay_item_dtbo_write</span><span class="params">(<span class="keyword">struct</span> config_item *item, <span class="type">const</span> <span class="type">void</span> *buf, <span class="type">size_t</span> count)</span></span><br><span class="line">&#123;</span><br><span class="line">    <span class="class"><span class="keyword">struct</span> <span class="title">dtbocfg_overlay_item</span> *<span class="title">overlay</span> =</span> container_of_dtbocfg_overlay_item(item);</span><br><span class="line"></span><br><span class="line">    <span class="keyword">if</span> (overlay-&gt;dtbo_size &gt; <span class="number">0</span>) &#123;</span><br><span class="line">        <span class="keyword">if</span> (overlay-&gt;id &gt;= <span class="number">0</span>) &#123;</span><br><span class="line">            <span class="keyword">return</span> -EPERM;</span><br><span class="line">        &#125;</span><br><span class="line">        kfree(overlay-&gt;dtbo);</span><br><span class="line">        overlay-&gt;dtbo      = <span class="literal">NULL</span>;</span><br><span class="line">        overlay-&gt;dtbo_size = <span class="number">0</span>;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    overlay-&gt;dtbo = kmemdup(buf, count, GFP_KERNEL);</span><br><span class="line">    <span class="keyword">if</span> (overlay-&gt;dtbo == <span class="literal">NULL</span>) &#123;</span><br><span class="line">        overlay-&gt;dtbo_size = <span class="number">0</span>;</span><br><span class="line">        <span class="keyword">return</span> -ENOMEM;</span><br><span class="line">    &#125; <span class="keyword">else</span> &#123;</span><br><span class="line">        overlay-&gt;dtbo_size = count;</span><br><span class="line">        <span class="keyword">return</span> count;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * dtbocfg_overlay_item_dtbo_read() - Read Device Tree Blob from Configuration Item</span></span><br><span class="line"><span class="comment"> * @item : Pointer to Configuration Item</span></span><br><span class="line"><span class="comment"> * @page : Pointer to Value for Store, or NULL to query the buffer size</span></span><br><span class="line"><span class="comment"> * @size : Size of the supplied buffer</span></span><br><span class="line"><span class="comment"> * return  Read Size</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="type">static</span> <span class="type">ssize_t</span> <span class="title function_">dtbocfg_overlay_item_dtbo_read</span><span class="params">(<span class="keyword">struct</span> config_item *item, <span class="type">void</span> *buf, <span class="type">size_t</span> size)</span></span><br><span class="line">&#123;</span><br><span class="line">    <span class="class"><span class="keyword">struct</span> <span class="title">dtbocfg_overlay_item</span> *<span class="title">overlay</span> =</span> container_of_dtbocfg_overlay_item(item);</span><br><span class="line"></span><br><span class="line">    <span class="keyword">if</span> (overlay-&gt;dtbo == <span class="literal">NULL</span>)</span><br><span class="line">        <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">if</span> (buf != <span class="literal">NULL</span>)</span><br><span class="line">        <span class="built_in">memcpy</span>(buf, overlay-&gt;dtbo, overlay-&gt;dtbo_size);</span><br><span class="line"></span><br><span class="line">    <span class="keyword">return</span> overlay-&gt;dtbo_size;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h4 id="2-2-2-dtbocfg-overlay-item-attr-status"><a href="#2-2-2-dtbocfg-overlay-item-attr-status" class="headerlink" title="2.2.2 dtbocfg_overlay_item_attr_status"></a><font size=3>2.2.2 dtbocfg_overlay_item_attr_status</font></h4><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * dtbocfg_overlay_item_status_store() - Set Status Attibute</span></span><br><span class="line"><span class="comment"> * @item:  Pointer to Configuration Item</span></span><br><span class="line"><span class="comment"> * @page:  Pointer to Value Buffer</span></span><br><span class="line"><span class="comment"> * @count: Size of Value Buffer Size</span></span><br><span class="line"><span class="comment"> * return  Stored Size or Error Status.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="type">static</span> <span class="type">ssize_t</span> <span class="title function_">dtbocfg_overlay_item_status_store</span><span class="params">(<span class="keyword">struct</span> config_item *item, <span class="type">const</span> <span class="type">char</span> *buf, <span class="type">size_t</span> count)</span></span><br><span class="line">&#123;</span><br><span class="line">    <span class="class"><span class="keyword">struct</span> <span class="title">dtbocfg_overlay_item</span> *<span class="title">overlay</span> =</span> container_of_dtbocfg_overlay_item(item);</span><br><span class="line">    <span class="type">ssize_t</span>       status;</span><br><span class="line">    <span class="type">unsigned</span> <span class="type">long</span> value;</span><br><span class="line">    <span class="keyword">if</span> (<span class="number">0</span> != (status = kstrtoul(buf, <span class="number">10</span>, &amp;value))) &#123;</span><br><span class="line">        <span class="keyword">goto</span> failed;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">if</span> (value == <span class="number">0</span>) &#123;</span><br><span class="line">        <span class="keyword">if</span> (overlay-&gt;id &gt;= <span class="number">0</span>) &#123;</span><br><span class="line">            dtbocfg_overlay_item_release(overlay);</span><br><span class="line">        &#125;</span><br><span class="line">    &#125; <span class="keyword">else</span> &#123;</span><br><span class="line">        <span class="keyword">if</span> (overlay-&gt;id  &lt; <span class="number">0</span>) &#123;</span><br><span class="line">            dtbocfg_overlay_item_create(overlay);</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> count;</span><br><span class="line">  failed:</span><br><span class="line">    <span class="keyword">return</span> -EPERM;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * dtbocfg_overlay_item_status_show() - Show Status Attibute</span></span><br><span class="line"><span class="comment"> * @item : Pointer to Configuration Item</span></span><br><span class="line"><span class="comment"> * @page : Pointer to Value for Store</span></span><br><span class="line"><span class="comment"> * return  String Size or Error Status.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="type">static</span> <span class="type">ssize_t</span> <span class="title function_">dtbocfg_overlay_item_status_show</span><span class="params">(<span class="keyword">struct</span> config_item *item, <span class="type">char</span> *page)</span></span><br><span class="line">&#123;</span><br><span class="line">    <span class="class"><span class="keyword">struct</span> <span class="title">dtbocfg_overlay_item</span> *<span class="title">overlay</span> =</span> container_of_dtbocfg_overlay_item(item);</span><br><span class="line">    <span class="keyword">return</span> <span class="built_in">sprintf</span>(page, <span class="string">&quot;%d\n&quot;</span>, overlay-&gt;id &gt;= <span class="number">0</span> ? <span class="number">1</span> : <span class="number">0</span>);</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h2 id="3-status属性的操作"><a href="#3-status属性的操作" class="headerlink" title="3. status属性的操作"></a><font size=3>3. status属性的操作</font></h2><p>我们向status写1的时候就可以开启设备树插件，我们来看一下怎么实现的，主要是看下面的函数：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * dtbocfg_overlay_item_status_store() - Set Status Attibute</span></span><br><span class="line"><span class="comment"> * @item:  Pointer to Configuration Item</span></span><br><span class="line"><span class="comment"> * @page:  Pointer to Value Buffer</span></span><br><span class="line"><span class="comment"> * @count: Size of Value Buffer Size</span></span><br><span class="line"><span class="comment"> * return  Stored Size or Error Status.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="type">static</span> <span class="type">ssize_t</span> <span class="title function_">dtbocfg_overlay_item_status_store</span><span class="params">(<span class="keyword">struct</span> config_item *item, <span class="type">const</span> <span class="type">char</span> *buf, <span class="type">size_t</span> count)</span></span><br><span class="line">&#123;</span><br><span class="line">    <span class="class"><span class="keyword">struct</span> <span class="title">dtbocfg_overlay_item</span> *<span class="title">overlay</span> =</span> container_of_dtbocfg_overlay_item(item);</span><br><span class="line">    <span class="type">ssize_t</span>       status;</span><br><span class="line">    <span class="type">unsigned</span> <span class="type">long</span> value;</span><br><span class="line">    <span class="keyword">if</span> (<span class="number">0</span> != (status = kstrtoul(buf, <span class="number">10</span>, &amp;value))) &#123;</span><br><span class="line">        <span class="keyword">goto</span> failed;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">if</span> (value == <span class="number">0</span>) &#123;</span><br><span class="line">        <span class="keyword">if</span> (overlay-&gt;id &gt;= <span class="number">0</span>) &#123;</span><br><span class="line">            dtbocfg_overlay_item_release(overlay);</span><br><span class="line">        &#125;</span><br><span class="line">    &#125; <span class="keyword">else</span> &#123;</span><br><span class="line">        <span class="keyword">if</span> (overlay-&gt;id  &lt; <span class="number">0</span>) &#123;</span><br><span class="line">            dtbocfg_overlay_item_create(overlay);</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> count;</span><br><span class="line">  failed:</span><br><span class="line">    <span class="keyword">return</span> -EPERM;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>当我们向 status 写入 1 的时候， 会执行 dtbocfg_overlay_item_create() 函数。 在这个函数中又去执行了  <a target="_blank" rel="noopener" href="https://elixir.bootlin.com/linux/v4.19.17/source/drivers/of/overlay.c#L844">of_overlay_fdt_apply()</a> 函数。 <a target="_blank" rel="noopener" href="https://elixir.bootlin.com/linux/v4.19.17/source/drivers/of/overlay.c#L844">of_overlay_fdt_apply()</a> 函数如下图 </p>
<img data-src="https://fanhua-picture.oss-cn-hangzhou.aliyuncs.com/01%E5%B5%8C%E5%85%A5%E5%BC%8F%E5%BC%80%E5%8F%91/02IMX6ULL%E5%B9%B3%E5%8F%B0/LV06-%E9%A9%B1%E5%8A%A8%E5%BC%80%E5%8F%91/LV06-12-ConfigFS-03-%E8%AE%BE%E5%A4%87%E6%A0%91%E6%8F%92%E4%BB%B6%E9%A9%B1%E5%8A%A8%E5%88%86%E6%9E%90/img/image-20250314153133971.png" alt="image-20250314153133971"  /> 

<p>设备树插件（dtbo） 里面的节点也要被转换成 device_node， 有的 device_node 也要被转换成 platform_device。 不过在进行转换之前， of_overlay_fdt_apply 函数会先创建一个改变集。 然后根据这个改变集去进行修改。  </p>
<p>创建改变集的目的是为了方便对设备树进行修改和复原。 设备树是一种静态的数据结构，一旦被编译和加载到内核中， 就难以直接修改。 为了解决这个问题， 设备树覆盖功能引入了改变集的概念。  </p>
<h1 id="二、改变集简介"><a href="#二、改变集简介" class="headerlink" title="二、改变集简介"></a><font size=3>二、改变集简介</font></h1><p>改变集是一个描述设备树变化的数据结构， 它记录了对设备树的修改操作， 如添加、 删除或修改节点。 通过创建改变集， 我们可以在运行时对设备树进行动态修改， 而无需修改原始的设备树源文件。  </p>
<p>通过创建改变集， 我们可以方便地定义需要进行的修改操作， 而不必直接操作设备树的底层结构。 这提供了一种高层次的抽象， 使我们能够以更简洁和可读的方式描述设备树的变化。同时， 改变集也可以被保存、 传递和应用到其他设备树上， 方便在不同系统或环境中进行设备树的配置和定制。  </p>
<p>此外， 改变集还可以用于设备树的复原。 在某些情况下， 我们可能需要在运行时撤销对设备树的修改并恢复到原始状态。 通过应用反向的改变集， 我们可以还原设备树， 使其回到修改之前的状态， 实现修改的复原。  </p>
<p>因此， 创建改变集提供了一种方便、 可控和可复原的方式来修改设备树， 使设备树的管理和配置更加灵活和可靠。  </p>

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            microseconds - 0-999之间的整数，做为date对象的毫秒数
            ==================================================*/
            var t1 = Date.UTC(2017, 
                              5, 
                              19, 
                              0, 
                              0, 
                              0); //北京时间
            var t2 = Date.UTC(todayYear,todayMonth,todayDate,todayHour,todayMinute,todaySecond);
            var diff = t2-t1;
            var diffYears = Math.floor(diff/years);
            var diffDays = Math.floor((diff/days)-diffYears*365);
            var diffHours = Math.floor((diff-(diffYears*365+diffDays)*days)/hours);
            var diffMinutes = Math.floor((diff-(diffYears*365+diffDays)*days-diffHours*hours)/minutes);
            var diffSeconds = Math.floor((diff-(diffYears*365+diffDays)*days-diffHours*hours-diffMinutes*minutes)/seconds);
            document.getElementById("sitetime").innerHTML="已在这里 "+diffYears+" 年 "+diffDays+" 天 "+diffHours+" 小时 "+diffMinutes+" 分钟 "+diffSeconds+" 秒";
        }
        siteTime();
    </script>



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